1. Field of the Invention
The present invention relates generally to a variable-delivery vane-type rotary compressor. More specifically, the present invention relates to a variable-delivery vane-type rotary compressor to be used as a refrigerant compressor for an air conditioner of a vehicle.
2. Description of the Background Art
In a variable-delivery vane-type rotary compressor which is well known in the art, a rotational displacement of an adjust plate relative to a front plate which fixedly closes a front end of a cam ring, is controlled by an adjust plate actuating mechanism in response to a pilot pressure applied to the adjust plate actuating mechanism from a pilot pressure applying mechanism, so as to adjust a compression starting point of a rotary vane in a working chamber provided in the cam ring.
A First Japanese Patent publication No. 62-265491 discloses such a rotary compressor. In this publication, the front plate is formed with a pair of induction ports and a pair of by-pass ports, and is further formed with a pair of pressure operation chambers. The adjust plate is formed with a pair of by-pass openings and is further formed with a pair of pressure receiving projections. Each pressure receiving projection is slidably fitted into the corresponding pressure operation chamber to divide it into first and second pressure chambers. The first chamber is communicated with an induction chamber through the by-pass port to bias the pressure receiveing projection in a first direction. The first chamber is further provided with a spring so as to bias the pressure receiving projection also in the first direction. The second chamber is communicated with a discharge chamber through a first passage formed in the compressor and is further communicated with a valve unit through a second passage. A third passage communicates the induction chamber to the valve unit and a fourth passage communicates a discharge chamber to the valve unit. The valve unit comprises a ball valve and a plunger which is arranged in the fourth passage and constantly receives a pressure within the discharge chamber to bias the ball valve in one direction. The ball valve also receives a bias force from a biasing unit through the third passage so as to be biased in the other direction opposite to the one direction. The ball valve opens and closes the communication between the induction chamber and the second chamber in response to a differential between the bias force applied by the biasing unit and the pressure within the discharge chamber applied through the plunger. Specifically, when the bias force applied by the biasing unit is larger to displace the ball valve in the other direction, the communication between the second chamber and the induction chamber is fully established through the second and third passages so that the pressure within the induction chamber is applied to the second chamber, i.e. the pressure within the second chamber applied from the discharge chamber through the first passage is released through the second and third passages into the induction chamber. Accordingly, the pressure within the induction chamber is applied to the second chamber as the pilot pressure to bias the pressure receiving projection in a second direction opposite to the first direction. On the other hand, when the pressure within the discharge chamber applied by the plunger is larger to displace the ball valve in the one direction, the communication between the second chamber and the induction chamber is blocked so that the pressure within the second chamber applied from the discharge chamber through the first passage is prevented from releasing. Accordingly, the pressure within the discharge chamber is applied to the second chamber as the pilot pressure to bias the pressure receiving projection in the second direction.
In response to a differential between the applied pilot pressure in the second chamber and the sum of the pressure within the induction chamber and the spring force in the first chamber, the pressure receiving projection slides in the pressure operation chamber in the first and second directions so as to control the rotational displacement of the adjust plate relative to the front plate to adjust the compression starting point of the rotary vane.
In the structure described above, however, since no pressure is applied through the fourth passage and through the second passage into the second chamber even when the communication between the second chamber and the induction chamber through the second and third passages is fully closed. This necessitates the first passage in addition to the fourth passage wherein the plunger is provided. Accordingly, the structure inevitably becomes complicated and costly.